Fuel conditioning apparatus



Sept. 18, 1934.

F. D. HOFFMAN FUEL CONDITIONING APPARATUS Original Filed Oct. 25, 1928 2Sheets-Sheet 1 I {'37 E 3 m 0 7 i I E 22 ///4 i 27 Z9 1 l 33 g 2 44 l 46v 4/ 46 u 2 47 {Z INVENTOR.

1 ATTORNEY F. D. HOFFMAN FUEL CONDITIONING APPARATUS Sept, 18,1934.

Original Filed Oct. 25, 1928 2 Sheets-Sheet 2 llll ATTORNEY ReissuedSept. 18, 1934 UNITED STATES PATENT OFFifiE'L FUEL CONDITIONINGAPPARATUS Fred D. Hoffman, Cleveland, Ohio, assignor, by mesneassignments, to Richard F. Kehr 13 Claims. (01. 11o 75) My inventionrelates to furnaces and more particularly to fuel conditioning apparatustherefor, the principalobjects of the'invention being to effectsubstantially complete combustion of fuels such as petroleum coke, hardor soft coal and tar, so as to obtain a maximum number of heat unitstherefrom, to effect efficient application of the resultant heat.

A correlative object is to prevent the formation of soot and escape ofunburned combustible gases by aerating and burning the combustibleproducts while in the furnace fire bowl. i

A more specific object is to direct a stream of preheated air onto theupper surface of the fuel bed in a manner such as to maintain theresultant burning mixture of gases evolved from the fuel and preheatedair in close heating proximity with the walls of the combustion chamberso as to utilize most effectively the resultant heat.

Another object is to provide a Venturi grate which is adapted to receiveair from outside of the furnace combustion chamber, conduct such air inheating proximity to the fire bed so as to preheat the same whilemaintaining it out of contact with the fuelbed, to freely expand the airthus preheated. so as to maintain the flow through the Venturi gratewhile at the same time reducing thevelocity prior to dischargetherefrom, and to discharge it as a more slowly moving forciblepreheatedstream uniformly onto the upper surface of the fuel bed. foreffecting .uniform surface combustion of the fuel and for eliminatinglocalized air currentsand consequent excessive rates of combustion oflocalized portions of the fuel bed.

Another object is to accomplish these results by means of a Venturigratewhichmay be manufactured economically and installed conveniently in thecombustion chamber of the usual types of furnaces without. requiring anysubstantial change in the furnace structures.

In accomplishing these and other objects I have provided improveddetails of structure, the preferred forms of which are illustrated inthe ac-' 5 Fig. 2 is a sectional view through the stoker conduit takenon a plane indicated by the line 2-2, of Fig. 1, illustrating the downdraft air inlet;

Fig. 3 is a sectional view through a preferred form of the Venturi gratepreheating device utilized for discharging combustion supporting airinto the furnace;

Fig. 4 is a horizontal section through the grate taken on a planeindicated by the line 44, Fig. 3:

Fig. 5 is a detail sectional view through the Venturi grate, taken on aplane indicated by the line 55,Fig.4;

Fig. 6 is a bottom plan view of the tuyere plate of the Venturi grate.

Referring in detail to the drawings: The invention is shown, forpurposes of illustration, in connection with a furnace 1, which may beof any type but is here illustrated as an ordinary warm air heatingfurnace including an ash pit 2, grates 3 mounted in a ledge 4 above theash pit, and a fire bowl 5 encircling the grate and provided at itsupper end with the usual radiator head 6 for passage of products ofcombustion to the outlet flue '7 opening to a chimney (not shown). Theash pit 2 is provided with the usual door 8 for admitting air into theash pit and through the grates 3 for supporting combustion-of the fuel,as in ordinary practice.

Positioned in alignment with the fuel door 9 of the furnace is aportable stoker and fuel conditioning apparatus 10 including aframe 11having legs 12 provided with rollers 13, and supported on the frame isfuel grinding apparatus 14 for pulverizing the fuel before it is fedinto the furnace.

The grinding apparatus includes a fuel receiving hopper 15, androtatably mounted in the bottom thereof are fuel crushing rolls .16 forgrinding lump fuel contained in the hopper. Rotatably mounted below therolls in a conduit 1'7 extending through the furnace door is av spiralconveyor 18 for feeding fuel pulverized by the rolls into the furnace.The conveyor is driven from a motor 19 carried by the frame, the motorbeing connected therewith through a gear reduction unit 20 which carriesa drive pinion 21 meshing with a gear 22 fixed on the conveyor shaft andwhich meshes with gears 24 fixed on the roller shafts 25.

The conveyor conduit extends to substantially the center of the furnaceand is provided with a diagonally cut end 2'7, through which the fuel isdischarged into the fire bowl.

In order to provide a down draft over the burning fuel and about thefresh fuel discharged from the conduit, I provide the conveyor conduitwith an outer coaxially mounted conduit 28 spaced therefrom andextending from a point adjacent the outer side of the fuel door to therality of openings 32; and to control the effective" port area of theopenings I provide a ringshapeddamper plate 33 having complementaryspaced openings 34 so that when the-openings inthe damper and theconduit are in registrationmax imum air inlet is provided but when thedamper is rotated to move the openings-out of registration, the amountof air may be reducedor err-. tirely cut ofi.

I prefer to control the damper 33 inconjuncr. tion with the damper 8 sothat when one is open, the other is closed and vice versa, bythermostatic regulation as now described.

' A thermostat controlled motor designated .35 is mounted on a; wall ofthe room-to be heated and the motor is provided with an actuating arm 36connected by a chain 37 with an arm Bf iprojectingradiallyfrom thedamper 33. Projecting from the damper diametrically opposite. to the arm3.8 is an arm 39 connected by achain 40 with the damper door in the ashpit. Thus when the thermostat raises the arm 38, the. damper is rotatedtobring the'port cpeni-ngsiinto registration to admit air through theconduit for draft over the-fuel, and at the'same time the damper 8 ismoved to closing position, shutting cit draftthrough the grates. Inorder to control theair passing'throug thergratesand preheat the air;and-also to-permit'free'passage of a portion of-air through the burning.fuel, I provide an air preheating and discharge device; comprisingVenturi shaped casting supported in upright position concentrically' of1 the" furnace. over the grates 3-; This casting, which formsa.Venturigrate; comprises anupright hollow shell, gradually contractedfrom its upper and lower-portionstoward an intermediate portion,preferably about: midway of the length of the shell, thus defining-aheatingcham'ber 41 which is gradually contracted upwardly into a shortthroat. 42:, and thence expanded upwardly forming a contiguouscommunicating expansion chamber 57, the purposes of which willlater bedescribed. The sh'ellis supported overthe grates by means of an ad'-justable spider 43. This spider may comprise hollow radial supports 44cast integral with the lower portion 45 of the'preheating compartment.Slidably mounted-in the supports"44 are legs ifi, each having a'downwardly projecting terminus eTproviding a foot. portion for restingon the wall portion of each radialsupport. is'an inwardly extendingtooth '52 for engaging in the notches of the legs so that whenthe-legsare moved to different positions inwardly and-outwardly of. the'snpport they will be latched to-the support member and held in theadjusted position.

The legs 46 are further provided adjacent their inner ends withlaterally projecting pins 53 and 54 which engage grooves 55 and 56 inthe inner sides; of the supporting members; so that when the Venturimember is resting on the flange, the pins bear on the lower faces of thegrooves and the notched portions of the arms bear against the teeth 52so that the legs are locked in engagement' therewith due to the weightof the Venturi grate.

Since the supporting members 44 are hollow and open attheirlower faceand communicate at their inner ends with the heating compartment 41 theyform in-efiect a part of this compartment zand'thuszincrease itscapacity especially when the legs are-drawn to their outermost positionfor. supporting the venturi in a large fire box.

-The expansion chamber of the Venturimember. isprovided atits upper endwith a tuyre plate, spaced, axially above the upper end of the expansionchamber so as .to define with the upper. periphery of the expansionchamber an discharge passage. This plate may be supported-.inthespacedrelationby means of a plurality of curved baffles 59 cast integrallywiththe. plate and bearing on the upper marginal portionof the inner. wallsurface the expansion chamben, thus. dividing theflannular. dischargepassage'into a plurality. of outlets 60 between adjacent. bafiles.

' The. operation of the venturiis substantially as follows: Assuming-theusualfire bed is provided in .the. firebowlaroundthe outside of theVonturi .grate-,. thev passage of air. through the grates 3 anddirectly. t-Qtheunder surface of the fuel bed is reduced.. due to .themore. easy access and passage. through the.Venturi'grate,-. but there isa sufficient. infiltration of. air. into. the. fire. bowl around. the.outside. .oflthe'. venturi to maintain the lower strata of. the fuel bedin a state of come bustion. Most of. the. air however passing into the.ash .pit I2 .dischargesthrough .the grates. 3. .into theinterior of theupwardly contractedheating chamber... 41. of. the Venturi. grate. Since.the Venturi grate. iscompletely surrounded by burn-. ing fnel', this ispreheated .to. a'high tempera.- ture, upon itsupwardpassage. throughthepreheating. compartment. by the. radiant heat. from the inner wallsurface of such compartment and by the passage. throughfthe interior ofthe sup: ports 44.. and legs 46.. ,The air passing upwardly through theheating compartment41 being thus preheated. to a. very. high degree. ofr temperature when it hasreachedtheuppe'rrlimitof saidcompartment,..tends to. expand. and would normally buildupalbackprlessurewhieh'would impede the flow of] air through. the.compartment 41.. and through the remainder. of. thegrate with. theprobable result .ot overheating the entire. grate. Sinceltheexpansionchamber 42 is flared o.utweirdly or: expanded. gradually.upwardly in the direction of movement of the. air it provides for atree. expansion of the preheated air. As a-result not only is.-thebackpressure which would otherwiseoccurin the chamber 41.-substantia1lyeliminated but the flow of air upwardly out through the topof thegrateis enhanced. In this and; causinga-mlative. cooling of' such walls. so

to maintain them below a temperature which would deleteriously affectthem. Also, localized intense fiows of air through the fuel bed from theunder side and over the fuel bed are eliminated.

If, during initial expansion, the entire quantity of air were dischargeddirectly into the fuel bed, localized currents would develop causingexcessive rates of combustion at localized portions of the bed withresultant overheating and fusing of the grates and furnace structureadjacent thereto and also fusion and clinkering of fuel on the gratesurfaces; Consequently, the expansion chamber is sufficiently long toallow for the initial rapid expansion so that when the air is dischargedinto the fuel bed it will pass thereinto as a large more uniform, moreslowly moving stream free from localized currents.

As the air passes into the upper end of the expansion chamber it isimpinged upon. the defiector of tuyre plate 58 and also on the baffles59 and is thereby deflected outwardly and discharged outwardly over thefuel bed with s. rotary or swirling motion. This air being preheated andswirling, readily mixes with the evolved gases within the fire bowl,assuring substantially complete aeration .and resultant combustionthereof before discharge from the fire bowl as well as preventingintense localized flow of air directly through the fuel bed. Thus thegases are regurgitated and burned, the swirling motion of the aircarrying them through a much longer path of travel before they leave thefire bowl. Since the air is discharged radially outwardly substantiallyall the evolved gases must pass through the air curtain thus formed sothat complete aeration of the gases is effected.

The air rising at comparatively high velocity through the expansionchamber 57 impinges on the interior of the tuyre plate 58 at acomparatively abrupt angle which tends to break the direct flow to someextent. However, since the air is being expanded freely in the lowerportion of the chamber 57 below the point of discharge and since thethroat 42 is comparatively short and so shaped as to cause a gradualconvergence and divergence of the walls of the shell at that portion,the retardation in velocity of flow of the out of the passages 60 doesnot appreciably retard the flow through the lower portion of theexpansion chamber 5'? nor through the short throat 42 and preheatingcompartment 41. Thus, by making the grate in venturi shape, a largeamount of air can be passed therethrough and the usual retardation dueto expansion such as is in straight tubes or other shapes of grates isnot present to any appreciable extent. It is therefore possible to passa large amount of air through the grate for cooling the same and toobtain the rapid and constant flow into the fire bowl. Since the grateis venturi shaped, there are practically no frictional losses or'lossesin head of the fluid and therefore the entire effective differential inhead between the outside air and the stack is utilized, this even beingassisted by virtue of the free expansion and consequent free rise of theair through the venturi.

I have found it desirable to control operation of the stoker conveyorfeed according to the room temperature by providing the thermostat 35with a switch for controlling current to the motor so that when thetemperature in the room has reached a desired degree, the thermostatwill shut off the motor through an electric circuit 61 to stop feed ofthe conveyor.

In operating mechanism constructed and assembled as described, thestoking apparatus may be wheeled to the fuel room and the hopper filledwith fuel, or the fuel may be placed in the hopper while the stokingapparatus is in functional relation with the furnace.

The motor may then be started to crush the fuel and feed it into thefurnace onto and around the air preheater. The fuel is then ignited, andthe draft through the grate being open, air passes upwardly therethroughto support combustion of the fuel. Part of the air enters the lower bellof the preheater, and passes upwardly through the venturi and outthrough the outlets 60, as above described, to commingle with thegaseous products of combustion and promote their combustion, so thatsaid gaseous products will be substantially completely burned beforepassing out of the furnace.

After the room has become sufiiciently warmed, the draft door 8 isautomatically lowered and the damper 33 for the down draft is opened bythe thermostat to maintain a steady slow burning fire.

I have found that the above described apparatus aids in the completecombustion of the fuel to provide for economic operation, as well as forthe elimination of smoke that otherwise would pass out of the chimney.

Having thus described my invention,

I claim:

1. In combination with a furnace including a fire bowl and a fuel feeddoor, stoking means including a horizontal conduit extending through thedoor substantially to the center of the fire bowl, means for admittingair upwardly through a fuel bed in the fire bowl to be dischargedconcentrically with the fuel discharged from the horizontal conduit, andmeans including an air supply conduit surrounding the first namedconduit and having a downwardly directed outlet surrounding thedischarge of the fuel conduit for delivering a downdraft around the.fuel moving downwardly from the fuel conduit.

2. 'In combination with a furnace including an ash pit provided with adamper, and stoker mechanism including a fuel conduit extending into thefurnace, a conduit for conducting a down draft of air coaxial with saidfuel conduit, a damper in said down draft conduit, a Venturi memberbelow the discharge of the fuel conduit for conducting air from the ashpit to the fuel bed, and thermostatically operated means including achain connected with said dampers for coincidently controlling thestoker mechanism and the air supplies.

3. In combination with a furnace including an ash pit provided with adamper, and stoker mechanism including a fuel conduit extending into thefurnace, a second conduit for conducting a down draft of air coaxialwith said fuel conduit, a damper in said down draft conduit, meansextending upwardly through the fuel bed and terminating at its upper endbelow the discharge of the fuel conduit operable to conduct air directlyfrom the ash pit through the fuel bed and to discharge said airabove'the fuel bed concentrically of the down draft, and means forcontrolling said dampers.

4. In a furnace having a combustion chamber and grates at the bottom ofthe chamber operable to support a fuel bed therein and to admit a r intothe fuel bed from the under side, a Venturi member comprising anelongated hollow shell body disposed in upright position in said chamberin intimate contact with said fuel bed and extending from the bottom ofthe fuel bed above the lab upper-surface thereof and open at the bottomto receive air at the lower end through the grates, said shell beinggradually contracted from each end toward an intermediate portion toform an elongated upwardly gradually contracted heating compartment anda communicating superimposed elongated gradually upwardly expandingexpansion compartment, whereby air entering the lower end of the Venturimember is. heated in the heating compartment and may expand freely inthe expansion compartment as it travels upwardly, deflecting means abovethe upper end of 'said expansion compartment in closely spaced relationto the expanding portion thereof for deflecting air discharging fromsaid expansion compartment laterally of the combustion chamber and-meanscocperable with said deflecting means for deflecting the air along aspiral path of travel.

5. In a furnace having a combustion chamber and grates at the bottom ofthe chamber operable to support a fuel bed therein and to admit air intothe fuel bed from the under side, azVenturi member comprising anelongated hollow shell body disposed in upright position in said chamberin intimate contact with said fuel bed and extending from the bottom ofthe fuel bed-to above the upper surface thereof and open'at the. bottomto receive air at the lower end throughthe grates, said shell beinggradually contracted from each end toward an intermediate portion toforman elongated upwardly gradually contracted heating compartment and acommunicating super imposed elongated gradually upwardly expandingexpansion compartment, said expansion compart merit having'imperforateside walls for the full length of the expanding portion thereof, wherebyair entering the lower end is heated in the heating compartment and mayexpand freely in the expansion chamber as it travels upwardly, air

vent'means at the upper end of said expansion compartment above theexpanding portion thereof operable to discharge air laterally from'saidexpansion compartment, and bafile means cooperable with said air ventmeans to deflect the dischargingair along a spiral path of travel.

6. In a furnace having a combustion-chamber and grates at the bottom ofthe chamber operable to support afuel bed therein and to admit air intothe fuelbed from the under side, a Venturi member comprising anelongated hollow shell bcdydisposed in upright position in said chamberin intimate contact with said fuel bed and extending from the bottom ofthe fuel bed .abov'the upper surface thereof and open at the bottomtoreceive air at the lower end through the grates,

said shell being gradually contracted from each end toward anintermediate portion to form an elongated upwardly gradually contractedheating compartment and a communicating superimposed elongated graduailyupwardly expanding expansion compartment, whereby air entering the lowerend of the Venturi member is heated in the heating compartment and mayexpand freely in the expansion compartment as it travels upwardly,

a deflecting cap, and a plurality of baffles inter spiral path oftravel.

'7. In-aiurnacehaying acombustion chamber and grates; at the bottom ofthe chamber operable to supporta fuel bed therein and to admit air intothe fuel bed from the under side, a Venturi grate comprising anelongated hollow shell body disposed in upright position in said chamberin intimate contact with said fuel bed and extending from the bottom ofthe fuel bed above the upper surface thereof and open at the bottom toreceive air atthe lower end through the grates, said shell beinggradually contracted from each end toward an intermediate portion toform an elongated upwardly gradually contracted heating compartment anda communicating superimposed elongated gradually upwardly expandingexpansion chamber whereby air entering the lower end is heated in theheating compartment and may expand freely in the expansion compartmentas ittravels-upwardly, means having a bafile wall at the upper: end ofsaid expansion compartment, passages intermediate said baffle Wall andthe upper endof'the compartment, the face of said baffle wall exposedtoward the interior of said expansion compartment projecting axiallytowardrthe expansion compartment at itscentral portion'and receding fromthe central portion radially of the wall from the expansion compartment,and bafies-onxsaid exposed face of said wall for deflecting the airimpinged on saidwail along 'a spiral path of travel, said bafilesterminating in spaced relation to each other at their inner ends.

8. In combination. with a furnace, and a stoker for dischargingfuel intothe furnace and having a fuel outlet therein, a Venturi member mountedbelow the outletfor admitting air to the furnace through the fuel. bed,a, tuyere plate above the Venturi member. for deflecting air impin ingthereon from the Venturimember outwardly from the grate, bafiies at theupper end of the Venturi member for deflecting said air along a spiralpath about the outlet, and. a conduit surrounding the fuel outlet forsupplying a downdraft in the furnace opposite to the Venturi member.

9. In combination with a furnace, a Stoker for dischargingfuel into thefurnace, a Venturi member mounted below the fuel discharge of the stokerfor admitting air to the furnace through the fuel bed, atuyre plateabove the Venturi member for de lecting air impinging thereon from "theVenturi member outwardly from the grate, -bafiles at the upper end ofthe Venturi member for deflecting said air along a spiral path about thefuel discharge, meansfor supplying a down draft in the furnace'oppcsiteto the first named supply of air; and means for alternately controllingthe said air supplies. I

10. In combination with a furnace feeding means including a conduitextending into the furnace substantially to the center thereof, aVenturimember mounted below the fuel discharge ofthe fuel feeding conduitforadmitting air to the furnace through the fuel b d, a tuyere plate abovethe Venturi member for deflecting air impinging thereon from the Venturimember outwardly from the grate, baffles at the upper end ofthe-Venturimember for deflecting said air along a spiral path about the.fuel discharge, andmeansincluding an air conduit s rounding the fuelfeeding conduit and having a downwardly directed outlet for supplying adown draft in the furnace opposite to the Venturi member.

11. In a furnace having a combustion chamber with grates at the bottomto support a fuel bed within the. chamber. and to admit air into thefuel 7 bed from the under side, a Venturi member comprising an elongatedhollow shell body disposed in upright position in said chamber inintimate contact with said fuel bed and extending from the bottom of thefuel bed to above the upper surface thereof, said member being open atthe bottom to receive air at the lower end and being graduallycontracted from the lower end toward an intermediate portion to form anelongated upwardly gradually contracted heating compartment and acommunicating superimposed compartment, means having a wall disposed inclosely spaced relation to the upper end of said latter compartment anddefining with the upper edge thereof a substantially peripheral passage,and bafile means disposed between said wall and latter chamber fordeflecting air discharging through said peripheral passage along aspiral path of travel.

12. In a furnace having a combustion chamber and means to support a fuelbed therein and to admit air into the under portion of the fuel bed, aVenturi member comprising an elongated hollow shell body disposed inupright position in said chamber in intimate heating relation andcontact with the fuel bed and extending from the lower portion of thefuel bed to above the upper surface thereof, said shell being openat thebottom to receive outside air and being gradually contracted from eachend toward an intermediate portion to form an elongated upwardlygradually contracted heating compartment, a superimposed elongatedgradually upwardly expanding expansion compartment, and a throat portionbetween and communicating with said compartments whereby air enteringthe lower end of the Venturi member is preheated in the heatingcompartment, passes through the throat portion and effects substantialcooling thereof with resultant preheating of the air and then passesfreely into the expansion compartment wherein it expands freely as ittravels upwardly, and air vent means of substantial cross sectional areaat the upper end of the expansion compartment to permit discharge of thepreheated air freely into the combustion chamber over the fuel bed.

13. In a furnace having a combustion chamber and means to support a fuelbed therein and to admit air into the under portion of the fuel bed, aVenturi member comprising an elongated hollow shell body disposed inupright position in said chamber in intimate heating relation andcontact with the fuel bed and extending from the lower portion of thefuel bed to above the upper surface thereof, said shell being open atthe bottom to receive outside air and being gradually contracted fromeach end toward an intermediate portion to form an elongated upwardlygradually contracted heating compartment, a superimposed elongatedgradually upwardly expanding expansion compartment, and a throat portionbetween and communicating with said compartments whereby air enteringthe lower end of the Venturi member is preheated in the heatingcompartment, passes through the throat portion and effects substantialcooling thereof with resultant preheating of the air and then passesfreely into the expansion compartment wherein it expands freely as ittravels upwardly, and a virtually annular passage of substantial crosssectional area at the upper end of the expansion compartment operable topermit discharge of said air freely laterally from said expansioncompartment into the interior of the combustion chamber.

FRED D. HOFFMAN.

